Absorbent articles such as bandages, disposable diapers, incontinent articles, feminine sanitary protection articles, and the like, typically incorporate an absorbent member, pad, panel, or core. The side of such an absorbent core which faces toward the body of the user is typically covered with a sheet or web of facing material which is liquid-permeable. The facing web may be a nonwoven fabric comprising a web of fibers strengthened with a polymeric binding agent. The facing web may also be a thermoplastic polymeric film.
Such facing webs can be made with suitable liquid permeability characteristics by employing one highly successful type of web-aperturing technology. Specifically, a liquid-impervious precursor web or starting web is supported on a three-dimensional forming member which has recesses into which the web is deformed and which has drain holes communicating with the recesses. A fluid, such as columnar streams of liquid, is directed against the web with a force sufficient to produce apertures in the web.
Typically, this process is efficiently effected by providing the forming member as a thin, annular sleeve mounted on a rotating drum below an array of small orifices from which columnar streams of liquid are discharged against the starting web as it is supported by, and carried on, the rotating drum. The liquid streams penetrate the starting web (as the apertures are formed), and the liquid then flows to the drum through drain holes in the forming sleeve. The liquid passes through openings at the periphery of the drum and into the interior of the drum where the liquid is collected by a sump and drain system. A vacuum may be applied to the sump and drain system to aid in removing the liquid.
The U.S. Pat. No. 5,567,376 discloses such a process for making a sanitary napkin covering, topsheet, or facing web in the form of an apertured, thermoplastic polymeric film. The apertured film has micro-holes defined by a network of fiber-like elements. The U.S. Pat. No. 5,685,301 (allowed U.S. patent application Ser. No. 08/590,099) discloses an apertured film made by a similar process which can be employed as a backing web which is especially suitable for use as a breathable backing sheet (as opposed to a facing sheet) of an absorbent article, such as a bandage or the like. U.S. Pat. No. 5,670,224 discloses a process for producing an apertured nonwoven fabric wherein a starting web of nonwoven material is supported on a forming member and subjected to columnar streams of liquid to create apertures in the web.
Although the above-discussed apertured film webs or nonwoven fabric webs function well in the products for which they are designed, it would be desirable to provide such apertured webs with improved liquid-permeability characteristics. It has been found that in some apertured webs, some of the apertures are not properly formed or are incompletely formed. In some cases, there may be small areas on the web in which the desired apertures have not been formed at all. This can have a deleterious effect on the capability of the web to accommodate the transfer of fluid through the web.
It has been found that failure to create apertures in a portion of a web, and the failure to produce completely and properly formed apertures in portions of the web, results from the blockage or partial blockage of the aperturing liquid flowing through the forming member. Typically, the forming member is an annular sleeve with drain holes as discussed above. The sleeve is mounted on a rotatable support frame or drum. The support frame or drum includes spaced-apart cross bars or support members around the periphery of the drum. The inside surface of the forming sleeve is supported by such spaced-apart bars or support members. Some of the forming sleeve drain holes can be partly or completely blocked by such support members. This prevents adequate drainage of portions of the forming sleeve.
In some cases, the liquid of the columnar streams can impinge upon the support member and splash back against the edge of an aperture formed in the web. This may cause the edge of the web aperture to be pushed outwardly so as to cause an "inversion" of a peripheral portion of the web around the aperture. It is typically desired that there be no such inverted areas of the web around the apertures so that the surface of the web facing the columnar jets of liquid remains free of projections or protuberances. Then, the web can be assembled as a facing sheet on the absorbent core so that the projection-free web surface faces away from the absorbent core of the completed product and faces toward the skin of the user. However, if portions of the web around some of the apertures are inverted and project outwardly against the skin of the user, then the user may perceive that as being uncomfortable. Accordingly, it would be desirable to provide an improved apertured web having properly formed apertures with a few or no inversion areas.
When a web is employed as a covering sheet, topsheet, or facing material for a sanitary napkin, it is desirable that the outwardly facing surface of the web (i.e., the surface of the web that contacts the user) should appear clean and dry to the user--even after menstrual fluid has flowed through the facing web. The designer of a sanitary napkin is faced countervailing considerations in attempting to design a facing web which appears clean and dry even after passing menstrual flow. On one hand, large apertures in the facing web allow menstrual fluid to quickly flow through the web to the absorbent core. On the other hand, apertures that are too large permit the fluid to be transported back from the absorbent core through the facing web and to contact the skin of the user. Furthermore, large apertures or open areas in the facing web permit the absorbed fluid or stain on the absorbent core to be seen through the facing web, and this may be perceived by the user as a failure of the absorbent product to work as well as it should.
Thus, in order to exhibit the desired clean and dry properties, a facing web or cover sheet of a sanitary napkin should have apertures that are large enough and numerous enough to rapidly accept a flow of menstrual fluid and to allow the flow to pass through the facing web to the absorbent core, but the apertures should be small enough and spaced far enough apart so as to mask the stain on the absorbent core and give the user a feeling of cleanliness. When an appropriate design has been determined for the aperture size, configuration, and spacing, it is important to manufacture the web so that the apertures are properly formed. If some of the apertures are not properly formed, or are not even formed at all, the total open area of the facing web will be less than is intended. Furthermore, if the facing web has an incompletely formed or poorly formed aperture, or has merely a depression where an aperture should be, such a defect can become a site which is likely to retain menstrual fluid and stain the facing web. Thus, it would be desirable to provide an improved facing web without such defects and to provide a process for making an apertured facing web without such defects.
Such defects may occur when apertures are created in a facing web on a forming sleeve supported on a rotating drum support structure wherein the support structure includes support bars of the type discussed above. Such support bars can prevent the columnar streams of liquid from effecting penetration of the portions of the web along a line above each of the support bars. This may create a "lines" of unapertured regions across the web. Even if a columnar stream of liquid penetrates a portion of the web above the underlying support bar, the resistance to the flow of the liquid through the system will be greatly increased owing to the blocking effect of the drum support bar. This can lead to poorly formed apertures.
The blockage of the columnar stream flow during the web aperturing process is of even greater concern when the web apertures are intended to be relatively large and produced by relatively large diameter columnar streams of liquid. For example, with one presently contemplated preferred form of an apertured web, it is desirable to employ columnar streams of liquid to form the apertures in a stretchable, thermoplastic, polymeric film. The liquid streams are discharged from orifices which have a diameter in the range of between about 0.010 inch and about 0.040 inch. This results in a relatively high liquid flow rate. With such a high flow rate, it is necessary to provide a relatively low resistance to the flow of liquid through the forming sleeve and underlying rotatable drum support structure so as to avoid marking or lining of the web material.
When making some types of apertured web materials, such as tricot fabric, the forming sleeve has relatively small drain holes. The small drain holes may each have a diameter which is considerably less than the width of the cross bars in the rotatable support drum on which the forming sleeve is mounted. Some of the drain holes can be completely blocked by the cross bars. This can prevent apertures from being formed in the web along the support bars, and this can create objectionable marks or lines in the apertured web which reduce the fluid transmission capability of the apertured web.
Accordingly, it would be desirable to provide an improved process for making an apertured web using columnar streams, especially columnar streams which discharge from orifices having diameters of 0.010 inch to 0.040 inch or greater, wherein the improved process eliminates, or at least substantially minimizes, the creation of poorly formed apertures as well as unwanted lines across the material in which no apertures are formed.